Prosthesis with feature aligned to trabeculae

ABSTRACT

A ball and socket joint prosthesis for use in arthroplasty is provided. The prosthesis includes a body for implantation at least partially within the medullary canal of a long bone. The long bone defines trabeculae in the proximal cancellous bone and lamellae in the cortical bone. The body includes a proximal portion thereof and a distal portion. The proximal portion has a medial periphery and includes surface features on a substantial portion of its proximal portion. The surface features are positioned to optimally transfer load from the prosthesis to the long bone.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of co-pending applications Ser. No.10/670,092 filed Sep. 24, 2003 and Ser. No. 09/989,123 filed Nov. 21,2001 issued as U.S. Pat. No. 6,652,591, which is based upon U.S.Provisional Patent Application Ser. No. 60/255,644 filed Dec. 14, 2000,entitled PROSTHESIS WITH FEATURE ALIGNED TO TRABECULAE. The disclosuresof U.S. Provisional Application Ser. No. 60/255,644 and U.S. applicationSer. Nos. 09/989,123 and 10/670,092 which are hereby totallyincorporated by reference in their entireties.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to the field of orthopaedics,and more particularly, to an implant for use in arthroplasty.

BACKGROUND OF THE INVENTION

The invention relates to implantable articles and methods formanufacturing such articles. More particularly, the invention relates tobone prosthesis and processes for manufacturing the same.

There are known to exist many designs for and methods for manufacturingimplantable articles, such as bone prosthesis. Such bone prosthesisinclude components of artificial joints, such as elbows, hips, knees,and shoulders. An important consideration in the design and manufactureof virtually any implantable bone prosthesis is that the prosthesis hasadequate fixation when implanted within the body.

Early designs of implantable articles relied upon the use of cementssuch as polymethylmethacrylate to anchor the implant. The use of suchcements can have some advantages, such as providing a fixation that doesnot develop freeplay or does not lead to erosion of the joining bonefaces postoperatively. However, the current trend is to use thesecements to a lesser extent because of their tendency to lose adhesiveproperties over time and the possibility that the cement contributes towear debris within a joint.

Recently, implantable bone prosthesis have been designed such that theyencourage the growth of hard tissue (i.e., bone) around the implant. Thebone attachment usually occurs and growth is promoted when the surfaceof the implantable bone prosthesis is irregular or textured. Theinteraction of newly formed hard tissue in and around the texturedsurface of the implantable bone prosthesis has been found to provide agood fixation of the prosthesis within the body. A greater degree ofbone fixation can usually be achieved where bone-engaging surfaces of animplantable bone prosthesis are more porous or irregular.

Porous or irregular surfaces can be provided in implantable articles bya variety of techniques. In some instance, an irregular surface patternor surface porosity is formed in an implantable bone prosthesis byembossing, chemical etching, milling or machining.

Another problem which has been observed in the use of known hip jointsystems relates to the proper distribution of stresses within theprosthesis and throughout the surrounding bone. If too little stress isapplied to the bone, resorption can occur leading to atrophy of theaffected area. Too much stress may also lead to resorption and atrophy,or may result in an undesirable hypertrophy of the affected area. Insome prior art, femoral stem designs excessive forces are transmittedthrough the relatively rigid stem to the distal portion, resulting inhypertrophy of the bone surrounding the distal portion, and atrophy ofthe bone surrounding the proximal portion of the stem. Accordingly,there exists a need for an improved hip joint prosthesis which addressesthese needs and other problems of prior hip joint designs.

Attempts have been made to provide for proximal loading of theprosthesis within the bone. For example, in U.S. Pat. No. 5,004,075 toVermeire a series of parallel spaced apart linear grooves 28 werepositioned perpendicular to the longitudinal axis 22 of the neck of theprosthesis. A second set of parallel spaced apart linear grooves 29 werepositioned generally perpendicular to the grooves 28. These groovesserve to provide support in the proximal region of the stem of thisprosthesis.

U.S. Pat. No. 4,865,608 to Brooker, Jr. a series of spaced apartparallel grooves 24 and 24′ were positioned along the outer periphery ofthe opposite sides of the proximal portion of the stem. The grooves werepositioned at an angle of approximately 70 degrees with respect to thelongitudinal axis of the stem.

In total hip arthroplasty, initial and long term success are achievedthrough the use of a device which is designed to provide at least twofeatures. The first of these features is the stable initial or immediatepostoperative fixation within the femur. The second feature is the meansto provide an optimal environment for a long-term stability in thefemur. In the past, fixation has been achieved through the use of bonecement, porous coatings and bio-ceramics. Bio-ceramics includes suchcompositions as hydroxyapatite and tricalcium phosphates. Many of thesecements, coatings and bio-ceramics have provided good clinical outcomes,however, none have addressed the biomechanics of load transmissionthrough the proximal femur.

Methods of achieving femoral fixation in the prior art have met withsome success. These methods include simple press fit, surface roughness,porous coating, and bio-ceramics. Many devices have included texturingto transfer load in favorable mechanical modes. However, none of theprior art devices have designed the texturing (steps) to transfer loadalong the natural load paths of the proximal femur. The Brooker patenthas angled steps on the anterior and posterior face, however, on themedial edge, the steps are longitudinal. This design will notappropriately transmit load to the medial calcar. The Vermeire patenthas no steps on the medial edge, posing a similar problem.

A commercially available product from Stryker Howmedica Osteonics knownas the Omni Fit Femoral Stem has normalization features which transmitload directly vertical. This load path is not natural. This device hasno medial steps. A commercially available product from DePuyOrthopaedics, Inc., the JMP S-ROM transmits axial loads, but again, doesnot follow the natural load path.

SUMMARY OF THE INVENTION

Accordingly, a need has arisen for a prosthesis which achieves fixationto the long bone by designing features to transfer load along thenatural load paths of the proximal long bone.

The present invention includes a proximal long bone prosthesis which hasbeen designed to provide initial stability and long term fixationthrough a series of features capable of transmitting load to theproximal long bone in a manner consistent with the natural load paths ofthe long bone. The long bone may be a femur, a humerus or any other longbone.

The present invention allows reconstruction of the proximal long bonewith a device that is specifically designed to provide stable initialfixation and long term stability by optimally transferring load alongthe natural load lines through the femur. The load paths through theproximal long bone are seen by both the alignment of the trabeculae inthe proximal cancellous bone and by the direction of the layers orlamellae in the cortical bone.

This device achieves initial fixation through a press fit. The press fitis achieved with a properly designed preparation instrumentation. Longterm stability is achieved through a series of steps which are alignednormal to the trabeculae of the proximal femur cancellous bone and thelamellae of the proximal femoral cortex. The steps transmit load normalto their surface and hence along the natural femoral load lines. Thisreplication of the natural femoral load paths lead to favorableremodeling of the proximal long bone. This fixation mode may be furtherenhanced with a bone in growth/on growth surface such as for examplesurface roughness, porous coating and/or bio-ceramics.

According to one embodiment of the present invention, a ball and socketjoint prosthesis for use in arthroplasty is provided. The prosthesisincludes a body for implantation at least partially within the medullarycanal of a long bone. The long bone defines trabeculae in the proximalcancellous bone and lamellae in the cortical bone. The body includes aproximal portion and a distal portion. The proximal portion has a medialperiphery and includes surface features on a substantial portion of theperiphery of the proximal portion. The surface features are positionedto optimally transfer load from the prosthesis to the long bone.

According to another embodiment of the present invention, a hip-jointprosthesis for use in arthroplasty is provided. The prosthesis includesa body for implantation at least partially within the medullary canal ofa long bone. The long bone has trabeculae in the proximal cancellousbone and has lamellae in the cortical bone. The body includes a proximalportion and a distal portion. The proximal portion has a medialperiphery and includes a plurality of ribs extending from a substantialportion of the periphery of the proximal portion. The ribs arepositioned so that the first direction of the ribs is from about 70degrees to about 110 degrees with respect to the trabeculae in theproximal cancellous bone, the normal lamellae in the cortical bone orthe medial periphery of the proximal portion of said body.

According to yet another embodiment of the present invention, a jointprosthesis for use in arthroplasty is provided. The prosthesis includesa body for implantation at least partially within the medullary canal ofa long bone. The long bone includes trabeculae in the proximalcancellous bone and lamellae in the cortical bone. The body includes aproximal portion and a distal portion. The proximal portion has a medialperiphery and includes surface features on a substantial portion of theperiphery of the proximal portion. The surface features are positionedto optimally transfer load from the prosthesis to the long bone.

According to a further embodiment of the present invention, a stem foruse in a joint prosthesis for implantation at least partially within themedullary canal of a long bone is provided. The long bone includestrabeculae in the proximal cancellous bone and lamellae in the corticalbone. The stem includes a proximal portion and a distal portion. Theproximal portion has a medial periphery and surface features on asubstantial portion of the periphery of the proximal portion. Thesurface features are positioned to optimally transfer load from theprosthesis to the long bone.

According to another embodiment a method for producing a jointprosthesis for use in arthroplasty is provided. The method includes thesteps of providing a body including a proximal portion and a distalportion, the proximal portion having a medial periphery thereof, placingsurface features on a substantial portion of the periphery of theproximal portion of the body, positioning the surface features tooptimally transfer load from the prosthesis to the long bone, andimplanting the prosthesis at least partially within the medullary canalof a long bone.

The technical advantages of the present invention include the ability totransmit loads to the proximal femur along the natural load lines. Theload lines or load paths through the proximal femur are seen by both thealignment of the trabeculae in the proximal cancellous bone and by thedirection of the lamellae in the cortical bone. This invention achievesinitial fixation through a press-fit achieved with properly designpreparation instrumentation. Long term stability is achieved through aseries of steps which are aligned normal to the trabeculae of theproximal femoral cancellous bone and the lamellae of the proximalfemoral cortex. The steps transmit load normal to their surface andhence along natural femoral load lines.

Another technical advantage of the present invention includes theability to provide long term stability and fixation by providing anenvironmental optimum for femoral bone remodeling. The long termstability achieved through the series of steps which are aligned normalto the trabeculae of the proximal femoral cancellous bone and thelamellae of the proximal femoral cortex transmit load normal to theirsurface and hence along the natural femoral load lines. This replicationof the natural femoral load paths leads to favorable remodeling of theproximal femoral bone. This fixation mode may be further enhanced with abone ingrowth or ongrowth surface, for example, by providing for surfaceroughness, porous coating and bio-ceramics.

Other technical advantages of the present invention will be readilyapparent to one skilled in the art from the following figures,descriptions and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in connection with the

FIG. 1 is a plan view of a hip prosthesis in accordance with anembodiment of the present invention;

FIG. 1A is a partial enlarged view of the hip prosthesis of FIG. 1showing steps on the periphery of the prosthesis in greater detail;

FIG. 1B is a partial enlarged view of the hip prosthesis of FIG. 1showing steps with an alternate construction to those of FIG. 1A on theperiphery of the prosthesis;

FIG. 1C is a partial enlarged view of the hip prosthesis of FIG. 1showing steps with an alternate construction to those of FIG. 1A on theperiphery of the prosthesis;

FIG. 1D is a cross-sectional view of FIG. 1 along the line D-D in thedirection of the arrows illustrating one of many possiblecross-sections;

FIG. 2 is a lateral end view of a hip prosthesis in accordance with theembodiment of the present invention of FIG. 1;

FIG. 2A is a cross-sectional view of FIG. 2 along the line A-A in thedirection of the arrows illustrating one of many possiblecross-sections;

FIG. 3 is a medial end view of a hip prosthesis in accordance with theembodiment of the present invention of FIG. 1;

FIG. 4 is a partial plan view of the hip prosthesis of FIG. 1;

FIG. 5 is a partial plan view of the hip prosthesis of FIG. 4;

FIG. 6 is a plan view of a hip prosthesis in accordance with anotherembodiment of the present invention;

FIG. 7 is a plan view of a shoulder prosthesis in accordance with afurther embodiment of the present invention;

FIG. 7A is a partial plan view of the shoulder prosthesis of FIG. 7showing an alternate stem-shoulder connection;

FIG. 8 is a plan view of a hip prosthesis in accordance with a furtherembodiment of the present invention;

FIG. 9 is a lateral end view of a hip prosthesis in accordance with theembodiment of the present invention of FIG. 8;

FIG. 10 is a medial end view of a hip prosthesis in accordance with theembodiment of the present invention of FIG. 8;

FIG. 11 is a plan view of a hip prosthesis in accordance with anotherembodiment of the present invention;

FIG. 12 is a lateral end view of a hip prosthesis in accordance with theembodiment of the present invention of FIG. 11; and

FIG. 13 is a medial end view of a hip prosthesis in accordance with theembodiment of the present invention of FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention and the advantages thereof are bestunderstood by referring to the following descriptions and drawings,wherein like numerals are used for like and corresponding parts of thedrawings. According to the present invention and referring now to FIG.1, joint prosthesis 10 is shown for use in arthroplasty. Arthroplasty isa well known procedure for the treatment of osteoarthritis. For afurther explanation of arthroplasty may be found in Charnley, Sir John.Low Friction Arthroplasty of the Hip. New York: Springer, Verlock,Berlin, and Heidelberg, 1979 incorporated herein by reference in itsentirety.

The joint prosthesis 10 is positioned in a long bone 12. While the longbone 12 may be any long bone within the human anatomy, the presentinvention is particularly well suited for long bones which have aarcuate shape particularly adjacent the resected portion of the bone.For example, the long bone 12 may be in the form of a humerus or, asshown in FIG. 1, a femur.

The femur 12 is resected along resection line 14 relieving the epiphysis16 from the femur 12. The epiphysis is shown as dashed line 11.

The prosthesis 10 is implanted in the femur 12 by positioning theprosthesis 10 in a cavity 20 formed by reaming a portion of cancellousbone 22 within medullary canal 24 of the femur 12.

The cavity 20 may be formed in the cancellous bone 22 of the medullarycanal 24 by either broaching or reaming or other similar techniques toremove the cancellous bone 22 from the canal 24. As shown in FIG. 1, thecavity 20 extends from metaphysis 26 into diaphysis 30 of the femur 12.

Any suitable combination of drilling, reaming or broaching can be usedto form a cavity which corresponds closely to the periphery of theprosthesis. Typically, a broach (not shown) is driven into the medullarycanal to form the cavity. This broach has a shape generally onlyslightly smaller than the portion of the implant that fits into thecanal 24 so that the prosthesis is press fitted into the cavity 20.

Preferably and as shown in FIG. 1, the prosthesis 10 includes a body orstem 32, a portion of which is positioned within the cavity 20 of thefemur 12, and a cup 34 which is connected to natural acetabulum 36. Thestem 32 is pivotally connected to the cup 34. The stem 32 may be indirect contact with the cup 34 or may, as shown in FIG. 1, include aliner or bearing 40 positioned between the cup 34 and the stem 32.

The cup 34 may be made of any suitable, durable material which iscompatible with the human anatomy. For strength and durability typicallythe cup 34 is made of a metal such as stainless steel, a cobalt chromealloy or titanium or may be made of a ceramic.

The liner 40 may be made of any suitable, durable bearing material andis often made of polyethylene for example ultrahigh molecular weightpolyethylene.

While the stem 32 may be made of unitary construction typically the stem32 includes a stem portion 42 and a head portion 44. The two-partconstruction of the stem 32 provides for easier manufacture and forproviding varying offsets for the prosthesis by utilizing a plurality ofhead portions 44 and/or a plurality of stem portions 42.

The stem portion 42 may be connected to the head portion 44 in anysuitable fashion. For example, the stem portion 42 may include a maletaper portion 46 which mates with a female taper portion 50 on the headportion 44.

As shown in FIG. 1, the stem portion 42 includes a proximal stem portion52, a distal stem portion 54 extending downwardly from the proximal stemportion, and a neck portion 56 extending upwardly from the proximal stemportion 52. The proximal stem portion 52 and the distal stem portion 54are located within the cavity 20 formed within the cancellous bone 22 ofthe medullary canal 24.

Hip prosthesis are secured to the medullary canal of the femur typicallyeither by a press-fit with the medullary canal or with the use of acement mantel which is positioned between the prosthesis and thecancellous bone. In utilizing a cement mantel the cavity is broached orreamed slightly larger than the stem and a quantity of cement (forexample, PMMA—polymethylmethacrylate) is placed within the cavity andthe stem inserted therein. A small uniform layer of, for example, 1-4 mmof cement is formed between the stem portion 42 and the femur 12. Whilethe present invention may have some value for use in prosthesis havingstems which utilize a cement mantel, the present invention is generallydirected toward a prosthesis having a stem which is press-fitted intothe cancellous bone.

As body load or weight is transferred through the torso from theacetabulum 36 to the femur 12 the load is transmitted along trabeculaeor load lines 60. These trabeculae or load lines 60 are positioned in adirection generally conforming to the length of the femur and are curvedin a direction toward the head of the femur.

In the diaphysis 30 or the more distal portion of the femur 12, the loadlines 60 are generally linear and run parallel to longitudinal axis 62of the femur 12. This is mainly due to the fact that the femur 12 withinthe diaphysis has a generally circular cross-section in a generallycylindrical shape.

On the other hand, within the metaphysis 26 the trabeculae or load lines60 have a curved or arcuate shape or path and digress continually fromthe longitudinal axis 62 in the proximal direction.

According to Wolff's Law, hypertrophy is defined as a thickening of thecortex with retention of normal cortical texture. According to Wolff'sLaw, the hypertrophy will occur at the area of highest stresssurrounding an implant. The thickening of the cortex caused by thehypertrophy is a very desirable event in the postoperative patient. Formany implants within a femur the location of hypertrophy is often at thedistal end of the implant. This is caused by the artificially raisedstress at the point of sudden transition from the flexible distal femurto the artificially stiffened proximal femur. This is true for bothpress-fit and cemented stems. This phenomenon of hypertrophy thusresults in excellent adhesion in the diaphysis but results in a lessthan desirable condition between the implant and the femur in themetaphysis.

To provide for the increased loading of the femur within the metaphysisand the resulted improvements caused by hypertrophy and Wolff's Law,according to the present invention surface features 64 are located onouter periphery 66 of the proximal stem 52. The surface features 64serve to increase the stress or load between the implant and the femurin the metaphysis 26 to thereby gain the benefit of Wolff's Law andhypertrophy within that portion of the femur.

Preferably, as shown in FIG. 1, the stem 32 has a shape generallyconforming to the shape of the femur 12. Thus, typically, within thediaphysis 30, the distal stem 54 is generally circular, having a shapegenerally similar to the circular shape of the femur within thediaphysis 30. Similarly, within the metaphysis 26, the proximal stem 52has a generally oval cross-section and an arcuate orientation in thedirection toward the acetabulum 32.

Further the proximal stem 52 becomes larger in the direction of theacetabulum 36. This curving, oval and enlarging toward the acetabulumconfiguration of the proximal stem provides a shape generally conformingto the cancellous bone within the metaphysis 26 of the femur 12.

According to the present invention and referring now to FIGS. 1, 4 and5, the applicants have found that the surface features 64 should bepositioned in an orientation to optimally transfer load between the stem32 and the femur 12.

Applicants have further found that the surface features 64 should bepositioned in an orientation relative to the load lines or trabeculae60. The load lines or trabeculae 60 pass through the proximal cancellousbone 22. The load lines 60 also pass through cortical bone or cortex 65.The cortical bone 65 has layers or normal lamellae 71 through which theload lines pass and which are concurrent therewith.

The orientation of the surface features 64 to the load lines 60 isdefined by angle α. Applicants have further found that the surfacefeatures 64 should be optimally positioned in an orientation generallynormal to the load lines or trabeculae 60 or that the angle α isoptimally around about 90 degrees.

While the benefit of positioning the steps in relationship to the loadlines or trabeculae are optimized when the steps are positionedgenerally normally or perpendicular to the load lines. It should beappreciated that the invention may be practiced where the steps 64 arepositioned less than an ideal 90 degrees or normal to the load lines.For example, the steps may be positioned from about 70 degrees to about110 degrees with respect to the trabeculae or load lines.

While the steps are optimally positioned generally normally orperpendicular to the load lines 60, it should be appreciated that everylong bone in every person's anatomy has a different anatomical shape.For example, referring to FIG. 1, the long bone may have a shape otherthan that of long bone 12. The long bone may have a shape as shown inlong bone 13 or as shown in long bone 15, both shown as dashed lines.

While it might be ideal to make an individual, customized prosthesiswith surface features designed and manufactured optimally normal to theload lines, this is probably not economically feasible. Applicants havethus found that the invention may, thus, be commercially practiced bydesigning the surface features 64 to be selected to be optimallypositioned generally normal to the load lines or to have at the surfacefeatures designed to be aligned around 70 to 110 degrees from the loadlimes for a average or normal femur or long bone. The outer periphery 66of the proximal stem 52 is typically designed to be positioned withinand to be spaced from and to conform generally to the inner periphery 67of the cortical bone 65 of an average femur or long bone. The outerperiphery 66 thus, preferably, generally conforms to inner periphery 67of the cortical bone 65 of the long bone to which it was designed.

Referring again to FIG. 1, since the load lines 60 pass through normallamellae of the cortex 65 and are concurrent therewith, the innerperiphery 67 of the cortex 65 is generally in alignment with the loadlines 60. As stated earlier, to optimized the positioning of the surfacefeatures 64, the features 64 are positioned normal to the load lines andthe inner periphery 67 of the cortex 65.

Thus, for an average long bone to which a prosthesis 10 is designed, theouter periphery 66 of the proximal stem 52 conforms generally to theload lines 60. Applicants have thus found that in commercially utilizingthis invention, the prostheses may be designed and manufactured with thesurface features positioned with respect to the outer periphery 66 ofthe proximal stem 52 of the prosthesis 10. Since the load exerted on theprosthesis is large around the proximal stem 52 at the center of theinner periphery of the medial portion of the proximal stem also known asmedial periphery 69 of the outer periphery 66, the Applicants havediscovered that the surface features 64 may be positioned with respectto the medial periphery 69 of the outer periphery 66

The surface features 64 form an angle β with medial periphery 69. Forexample, the surface features may be positioned from about 70 degrees toabout 110 degrees with respect to the medial periphery 69 of theproximal stem 52 of the prosthesis 10. The surface features 64 mayoptimally be positioned in an orientation generally normal to the medialperiphery 69 or the angle β may optimally be around about 90 degrees.

Thus, as shown in FIG. 1, in the portion of the metaphysis 26 next tothe diaphysis 30, the surface features 64 run generally perpendicular tothe load line 60 and also nearly perpendicular to the longitudinal axis62. Conversely in the portion of the metaphysis 26 further from thediaphysis 30, the surface features 64 run generally perpendicular to theload line 60, but far from being perpendicular to the longitudinal axis62.

The surface features 64 are generally in the form of grooves, ribs orridges extending inwardly or outwardly from the surface 66. The surfacefeature 64 generally has a uniform cross-section as shown FIGS. 1Athrough 1C.

Applicants have found that by positioning the surface feature 64 in anorientation generally perpendicular to the load line 60 the supportingability of the surface features 64 may be optimized. By optimizing theload capacity of the surface feature 64, the stress imparted from thestem 32 to the femur 12 may maximize the stress at that position.Further, because Wolff's Law encourages hypertrophy or the thickening ofthe cortex in the metaphysis 26 of the femur 12, the adherence and bonegrowth around the implant within the metaphysis area 26 is therebyimproved.

The applicants have found that a large portion of the load transferredby the stem is concentrated in that portion of the stem adjacent themore curved portion of the femur 12.

For example, referring now to FIG. 2A, a typical cross section of theproximal stem 52 of the prosthesis 10 is shown. It should be appreciatedthat the proximal stem 32 may have any suitable cross section. Since thecross section of the proximal portion of the long bone 12 is typicallyoval or non-circular, a non-circular prosthesis cross section ispreferred. The shape of FIG. 2A is pentagonal or five sided with a largesemicircular portion on the medial side.

The surfaces 70, 72 and 74 which approximate the curved portion of thefemur 12 transfer a major portion of the load between the femur 12within the metaphysis 26. Applicants have found that if the surfacefeatures 64 are positioned generally normal or perpendicular to the loadlines 60 on surfaces 70, 72 and 74 a large majority of the benefit ofproviding the surface features generally normal to the load lines may beaccomplished. Thus the surface features 64 located on other surfaces,for example, surfaces 76, 80 and 82 may be oriented in directions otherthan normal to the load lines or surface features 64 may be omitted fromthe surfaces 76, 80 and 82.

Referring now to FIG. 1A, to optimize the load carrying or stressincreasing capacity of the surface features 64, the surface features asshown in FIG. 1A may be in the form of steps or terraces. Such steps orterraces are more fully shown in U.S. Pat. No. 4,790,852 to Noiles andincorporated herein by reference in its entirety. The terraces 64 havean inner edge 84 and an outer edge 86. A ledge 90 is formed betweenouter edge 86 and inner edge 84. The ledge is positioned distally andserves to provide optimum support or stress for the stem 32. Theterraces 64 has a vertical spacing -V- between terraces of approximately0.50 to 3.0 mm and a depth -D- of approximately 0.2 mm to 1.5 mm.

It should be appreciated that while the terraces 64 as shown in FIG. 1Aare preferred, the invention may be practiced with other types ofsurface features. For example, as shown in FIG. 1B, the surface featuresmay be in the form of ribs 164 which provide an angled support surface190.

Alternatively referring to FIG. 1C, the surface features may be in theform of grooves 164′ which extend inwardly from the surface.

To further promote bone growth between the stem and the femur andreferring again to FIG. 1A, the surface 66 of the surface features 64may be coated by a coating 92. The coating 92 may be any coating whichpromotes bone growth and/or interconnections between the prosthesis andthe femur. For example the coating 92 may be a bio-ceramic. Suchsuitable bio-ceramics include hydroxyapatite or tricalcium phosphates.Alternatively, the coating 92 may be a porous coating. Alternatively,the coating may be a porous coating and a bioceramic coating incombination.

Various porous coatings have found to be very effective. Oneparticularly effective coating is sold by the Assignee of the instantapplication under the tradename Porocoat. The Porocoat coating is morefully described in U.S. Pat. No. 3,855,638 to Pilliar and herebyincorporated herein by reference in its entirety.

This porous coating consists of a plurality of small discreet particlesof metallic material bonded together at their points of contact witheach other to define a plurality of connected interstitial pores in thecoating. The particles are of the same metallic material as the metallicmaterial from which the substrate is formed. Examples of suitablematerial include austenitic stainless steel, titanium, titanium alloysand cobalt alloys.

The stem 32 may be made of any suitable durable material and, forexample, may be made of a titanium, a cobalt chrome molybdenum alloy orstainless steel. The applicants have found that titanium TI-6AL-4V iswell suited for this application.

It should be appreciated that while, as shown in FIG. 1, the proximalstem 52 has a taper design, the aligning of surface features withrespect to the load lines of the present invention may be practiced withthe taper design or with a non-taper design. Further it should beappreciated that while, as shown in FIG. 1, the prosthesis 10 is shownwith a coating 92, the invention may be practiced without the porouscoating 92.

The terraces 64 are aligned in a direction generally normal to themedial curve or load line 64 on the anterior face 70, the medial arcuatesurface 74 and the posterior surface 72. The terraces 64 becomehorizontal as they approach the lateral aspect of the implant, (surfaces76, 80 and 82) (see FIG. 2A) to align roughly normal to the lateral faceof the implant.

Referring now to FIG. 2, the stem 32 is shown in an anterior/posteriorview. The stem 32 is shown with the distal stem 54 not including thesurface features or terraces 64. The proximal stem 52 however includesthe terraces 64 on posterior lateral surface 76 and on anterior lateralsurface 80. As shown in FIG. 2, the proximal stem 52 does not haveterraces 64 in the lateral surface 82.

As shown in FIG. 2 the terraces 64 on the posterior lateral surface 76and the anterior lateral surface 80 are generally perpendicular tolongitudinal axis 62. It should be appreciated that the terraces 64 onsurfaces 76 and 80 may be positioned normal to the load lines 60.However, since most of the benefit of the positioning of the surfacefeatures 64 normal to the load line 60 is accomplished on surfaces 70and 72, for simplicity of design and manufacture, the terraces 64, asshown in FIG. 2, may be positioned normal to the longitudinal axis 62.Further, for simplicity and ease of manufacture, the lateral surface 82,as shown in FIG. 2, may be made without terraces 64.

Referring now to FIG. 3 the stem 32 is shown in a posterior/anteriorposition. The medial surface 74 is shown with terraces 64 on surface 66in the proximal stem 52. The terraces 64 are positioned normal to loadlines 60.

As shown in FIG. 3 the distal stem 54 may include a polished tip 94extending a distance of, for example, one-half to one inch from thedistal end of the stem 32. The distal stem 54 may, for example, be gritblasted in the remaining portion 96 of the distal stem 54.

Referring now to FIG. 6, an alternate embodiment of the presentinvention is shown as prosthesis 210. Prosthesis 210 is similar toprosthesis 10 of FIG. 1 except that, whereas prosthesis 10 of FIG. 1includes a separate stem and head which are connectable together, theprosthesis 210 includes a head portion 244 which is integral with stemportion 242. Prosthesis 210 includes stem 232 which is pivotallyconnected to cup 234 and includes a bearing or liner 240 placedtherebetween.

As with prosthesis 10, prosthesis 210 includes steps 264 similar tosteps 64 of prosthesis 10 which steps 264 are positioned generallynormal or perpendicular to load lines or trabeculae 260. As in theprosthesis 210 the steps 264 are positioned on the proximal stem 252 ofthe stem 232. The steps 264 are preferably similar to the steps 64 ofthe prosthesis 10 of FIG. 1.

Referring now to FIG. 7 an alternate embodiment of the present inventionis shown as shoulder prosthesis 310. The shoulder prosthesis 310includes a stem 332 which is implanted into a humerus (not shown). Theprosthesis 310 also includes a head portion 344 attached to the stem322. The head portion 344 may be secured to the stem 322 in any suitablemanor and may alternatively be integral therewith. The head portion mayhave a external taper 346 extending therefrom which mates with aninternal taper 350 in the stem 332.

Such a configuration is shown in U.S. Pat. No. 5,314,479 to Rockwood etal. incorporated by reference herein in its entirety. The stem portion342 of the stem 332 includes a proximal stem 352 and a distal stem 354.For the same reasons expressed with regard to the prosthesis 10 of FIG.1, the prosthesis 310 includes steps 364 similar to the steps 64 of theFIG. 1 prosthesis. The steps 364 are aligned generally perpendicular ornormal to the trabeculae or load lines 360. For the same reasonsexpressed with regard to the FIG. 1 prosthesis 10, the steps 364 arepreferably positioned on the proximal stem 352.

Referring now to FIG. 7A, a alternate securing arrangement is shown forconnecting the head portion to the stem. In this arrangement the stem332′ may have a external taper 346′ extending therefrom which mates withan internal taper 350′ in the head portion 344′. Such a configuration isshown in U.S. Pat. No. 6,120,542 to Camino et al. incorporated byreference herein in its entirety.

Another embodiment of the present invention is shown in FIGS. 8 through10 as stem portion 432. Stem portion 432 is similar to stem portion 32of the FIG. 1 prosthesis except that the proximal stem 452 of the stemportion 432 includes steps 464 similar to the step 64 of the prosthesis10 which steps 464 are positioned completely around the periphery of theproximal stem 452.

Referring now to FIG. 8, the stem portion 432 includes the distal stem454, the proximal stem 452 and neck portion 456. The steps 464 arepositioned completely around the periphery of the proximal stem 452. Infact the steps 464 are positioned on the anterior face 472, the anteriorlateral face 480 and the posterior face 470.

Referring now to FIG. 9 the steps 464 are positioned on the posteriorlateral face 476, on the lateral face 482 and on the anterior lateralface 480.

Referring now to FIG. 10 the steps 464 are also positioned on the medialface 474 of the proximal stem 452.

Referring now to FIGS. 11, 12 and 13 a further embodiment of the presentinvention is shown as a stem portion 532. Stem portion 532 is similar tostem portion 32 of the FIG. 1 prosthesis except that steps 564, whichare similar to steps 64 of the FIG. 1 prosthesis, are positioned only onthe anterior, posterior and medial faces.

Referring now to FIG. 11, the stem portion 532 includes a distal stem554, a proximal stem 552 and a neck portion 556. The steps 562, similarto the steps 64 of the FIG. 1 prosthesis 10, are positioned only on theproximal stem of 552. The Applicants have found since the loading on thestem portion 532 is primarily on the anterior, posterior and medialfaces, the invention may be practiced with steps 562 positioned only onthese faces. In fact, the invention may be practiced with the steps onperhaps less than these three faces.

As shown in FIG. 11 the steps 562 are located on the medial face 574,the posterior face 570 and the anterior face 572. The anterior lateralface 580, as shown in FIG. 11, does not include the steps 564.

Referring now to FIG. 12, no steps 562 are positioned on the posteriorlateral face 576, on the lateral face 582 and on the anterior lateralface 580.

Referring now to FIG. 13 the medial face 574 of the proximal stem of 552includes these steps 564.

By providing a prosthesis which has a stem with steps which are alignedin a direction generally normal to the load lines or trabeculae of theprosthesis load carrying capacity of the proximal femur may beoptimized. By optimizing the loading of the proximal femur, amanifestation of Wolff's Law can occur which causes the raised stressesat the greatest loading to create a thickening of the cortex andimprovement of the bone growth and adherence of the prosthesis to theproximal femur.

By providing a prosthesis having surface features in the form of stepswhich are positioned generally normal to the load lines of theprosthesis, the prosthesis may benefit from a long term stability andfixation by providing an environment optimum for femoral boneremodeling.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions, andalterations can be made therein without departing from the spirit andscope of the present invention as defined by the appended claims.

1. A ball and socket joint prosthesis for use in arthroplasty comprising: a body for implantation at least partially within the medullary canal of a long bone defining trabeculae in the proximal cancellous bone thereof and defining lamellae in the cortical bone thereof, said body including a proximal portion thereof and a distal portion thereof, said proximal portion having a medial periphery thereof, said proximal portion including surface features thereof on a substantial portion of said proximal portion, said surface features being positioned to optimally transfer load from the prosthesis to the long bone, wherein said surface features are elongated in a first direction of said features; and wherein said surface features are positioned so that the first direction of said features are from about 70 degrees to about 110 degrees with respect to the proximal portion of said body.
 2. The joint prosthesis of claim 1: wherein said surface features are elongated in a first direction of said features; and wherein said surface features are positioned so that the first direction of said features are substantially normal to the medial periphery of the proximal portion of said body.
 3. The joint prosthesis of claim 2: wherein said surface features comprise a plurality of ribs elongated in a first direction of said features.
 4. The joint prosthesis of claim 3, wherein the ribs comprise steps.
 5. The joint prosthesis of claim 4, wherein at least a portion of the surface of said ribs is adapted to enhance bone growth thereto.
 6. A joint prosthesis for use in arthroplasty comprising: a body for implantation at least partially within the medullary canal of a long bone defining trabeculae in the proximal cancellous bone thereof and defining lamellae in the cortical bone thereof, said body including a proximal portion thereof and a distal portion thereof, said proximal portion having a medial periphery thereof, said proximal portion including surface features thereof on a substantial portion of the medial periphery of said proximal portion, said surface features being positioned to optimally transfer load from the prosthesis to the long bone wherein said surface features are elongated in a first direction of said features.
 7. The joint prosthesis of claim 9: wherein said surface features comprise a plurality of ribs elongated in a first direction of said features.
 8. The joint prosthesis of claim 10, wherein at least a portion of the surface of said ribs is adapted to enhance bone growth thereto.
 9. The joint prosthesis of claim 11, wherein at least a portion of the surface of said ribs comprises at least one of a surface roughness, a porous coating and a bioceramic.
 10. A stem for use in a joint prosthesis for implantation at least partially within the medullary canal of a long bone defining trabeculae in the proximal cancellous bone thereof and defining lamellae in the cortical bone thereof, comprising: a distal portion thereof; and a proximal portion thereof, said proximal portion having a medial periphery thereof, said proximal portion including surface features thereof on a substantial portion of the medial periphery of said proximal portion, said surface features being positioned to optimally transfer load from the prosthesis to the long bone, wherein said surface features are elongated in a first direction of said features, and wherein said surface features are positioned so that the first direction of said features are from about 70 degrees to about 110 degrees with respect to the medial periphery of the proximal portion of said body.
 11. The stem of claim 13: wherein said surface features are elongated in a first direction of said features; and wherein said surface features are positioned so that the first direction of said features are substantially normal to at least one of the trabeculae in the proximal cancellous bone, the normal lamellae in the cortical bone and the medial periphery of the proximal portion of said body.
 12. The stem of claim 13: wherein said surface features comprise a plurality of ribs elongated in a first direction of said features.
 13. The stem of claim 15, wherein the ribs comprise steps.
 14. The stem of claim 15, wherein at least a portion of the surface of said ribs is adapted to enhance bone growth thereto.
 15. The stem of claim 17, wherein at least a portion of the surface of said ribs comprises at least one of a surface roughness, a porous coating and a bioceramic. 